I noticed that the otherwise very unseful IATE terminology provider App somehow makes the IATE Termbase into the default terminology provider at random points in mid-project. Maybe the team can once look into this.
Just replying here to bring this thread to the top of the list and see if anyone else is experiencing the same issues.
Thanks Steven Whale
it's more general, so I started this thread instead: https://community.sdl.com/product-groups/translationproductivity/f/studio/27451/default-termbase-keeps-switching